Bucking/ Cutting Out When Cold/ high idle

[dvn1129]

Hello all,
I have a 1986 Ranger 2.9l 2wd 5spd. The last 6 months or so, whenever I start it with the engine cold, my truck jerks and litterally throws me back and forth when accelerating. For a while, I just learned to deal with it, but it's getting worse now. Around 2000 RPM's the engine hesitates, and for a split second seems to cut off. It'll rev freely to the 2-2400 range, then stop for a hair, drop a hundred or so rpms, then' rev just fine once you get it past the 2400 range. I was leaning torward it being some sort of weird drivetrain/clutch engagement quirk, but I've recently discovered that when in neutral, the engine does the same cut out/ stumble. No jerking of the truck since the RPM inconsistancies don't reach the drive train. Also, When it is warmed up, it will idle high (aroung 15-1700 range. My solution for this is to quickly cycle the key off and back on which brings the idle back down toward 900. Maybe the problems are linked? Please help me figure this one out! I love this truck, and am in the process of painting it and when it looks excellent, I would like it to drive as such.

 

[Earl43P]

Welcome to The Ranger Station!


A common failure is the ignition module (ICM), mounted on your distributor.

Another is the fuel pump relay and PCM relay. I wouldn't rule out a bad fuel pressure regulator either. That can be tested by removing its vacuum line and listening for an idle change. No change would make it bad.

Might want to check the timing too (or simply mark the distibutor, then move it from that mark a bit and see how/if it affects the problem).

 

[dvn1129]

Why would the ICM cause it only when it was cold? I do believe my ICM is shorting though. Backing out of a parking space at my work last month, the ranger died. I tried to get it to start, then gave up and got a ride from a co worker. The next day we started doing some testing and realized it wasn't sparking, so i slapped a new coil on it because the coil was getting good voltage in and a good ground, yet wasn't working. I decided to make sure the center dizzy plug hadn't fallen out some how and accidentally bumped the wires into the ICM, and the fuel pump kicked on, and it fired right up. I got curious, and left it running and messed with the wires again, and it promptly died. What makes me curious is this whole time throughout this, I could go from key off to on and it would prime just fine. I wonder what the ICM has to do with priming the fuel system? Could the ICM make it run weird cold, then when everything warms up start working properly again?

 

[kimcrwbr1]

The ICM is in closed loop when it it cold is why it is different. Disconnect the battery and clean all the electrical connectors good and use some dielectric grease on them when you put them together. Pull the idle air control off the throttle body and clean it good along with the throttle body, open the butterfly and wipe everything down good with a gas rag along with the hole the IAC goes into. pull the IAT intake air temp sensor in the plenum and clean it good with elect cleaner or rubbing alcohol. Put everything back together and make sure all the sensors are plugged in before you start it. If it still runs like ass your gonna want to pull the codes the tech library has all that info but give all the wiring a good once over clean the IAT, TB and IAC good and put a new PCV in it then see how it runs. Do not attempt to clean the PCV just replace it every time you replace the plugs. Oh yea how old are the plugs rotor and cap. Do all the preventive maint first then you can troubleshoot if necessary.

 

[kimcrwbr1]

If you dont know how old the plug wires are replace them!

 

[Ranger Blake]

mine was doing this when i first got it. there was a disconected vaccum hose and a loose ground wire. fixed that and problem solved

 

[lost86broncoii]

Not to steal the thread, but which ground wire did you fix Ranger Blake?
(my 86 is bucking and jerking too, and also when I touched my ICM wiring it primed the fuel pump once as well)